Grinding oil containing pyrophosphatidic acid and sulfur



GRINDING 01L CQNTAINING PYROPHOS- PHATEDIC ACID AND SULFUR Harold. W.Johnston, Cleveland Heights, Ohio, assignor to The Standard Gil Company,Cleveland, Ohio, a corporation of (thin 4 Claims. (Cl. 252-461 Thisinvention relates to grinding oils of a superiornature, moreparticularly to improved grindingoil compositions which greatly increasethe life of abrasive wheels and reduce temper color formation and to amethod of grinding with such oils.

Grinding oils are used when grinding metal with-an abrasive grindingwheel and are to be distinguished from cutting oils. Some oils which aregood for cutting purposes are not good for grinding and vice-versa. Acutting oil is generally used in cutting steel or othermetalwith acutting tool such as in a lathe whereas a grinding oil is used ingrinding steel or other metal with an abrasive wheel or with a looseabrasive. The' grinda'bility of steel is extremely sensitive to the typeof grinding oil used particularly under severe conditions of operation;

in plant practice where articles are being manufactured by a processinvolving a grinding step, the grindingoil.

used is often a very important part of the economics of the operation. Aprimary consideration in most grinding operations is wheel wear becauseexcessive wear. results in changes of dimension of the article outsidethe specification limits. Wheel wear is customarily measured in terms ofwheel life, i. e., the number of parts which may be ground before itbecomes necessary to replace or redress the grinding wheel. Any grindingoil. which will increase wheel life is an important asset tomostgrinding operations because it will lower the number of wheelsrequired and consequently lower the processing cost.

It has been discovered that the rate ofwheel wear is greatly dependenton the nature of the lubricant employed and it has been found that wheellife may be considerably prolonged by the use of the grinding oils ofthis invention.

The principal object of this invention is the provision of grinding oilcompositions containing certain prescribed additives by the use of whicha great increase in wheel life and a reduction in temper color formationareobtained. A second object is the provision of a method. of using thenew compositions. Other objects willbecome apparent as the invention isdescribed hereinafter.v

in the past, it has been proposed to add pyrophosphatidic acid togrinding oils for the purpose of reducing temper color formation. It hasalso been proposed to add sulfur to grinding oils. However, as far as isknown, thereis no suggestion in the prior art that the two additives maybe combined in a grinding oil formulationp According to this inventionit has been found that a combination of the two additives in a grindingoil base results in unforeseen advantages.

The grinding oil compositions of this invention comprise a majorproportion of a grinding oil base and, as additives thereto, minorproportions of pyrophosphatidic acid and sulfur. A preferred grindingoil compositionis that comprising at least 88 weight per centof av baseoil which is composed of at least 90 weight per cent of a mixture of anamount of a mineral oil of viscosity not over 100 SUS (Saybolt Universalseconds) at 100 F. within the range of 53 to 95 weight per cent and annited States Patent amount of a mineral oil of 2000 to 6000 SUS at 100F. within the-range -of47 to 5 weight per cent to provide a viscosityinthe range of 150 to 300 SUS at 100 F., from about 0.5 to about 10 percent by weight of pyrophosphatidic acid and from about 0.25 to about 3.0per cent lily-weight of sulfur.

The method of this invention comprises grinding metal with an abrasivein the presence of a grinding oil of the composition described above;

Pyrophosphatidic acid is essentially the fatty ester of pyrophosphoricacid and it has the formula:

Into a suitable vessel are placed 70 parts of a conventionally refinedpetroleum oil having a viscosity of SUS 'at F. Into the conventionallyrefined oil there is dissolved 0.56 parts (0.8% of the conventionallyrefined oil) of sulfur. There is then blended in 28 parts of a so-calledbright stock oil having a viscosity of SUS at 210 F. and 2 parts ofpyrophosphatidic acid. The order of addition is not critical. The twooils from the base and the sulfur and pyrophosphatidic acid comprise theadditives.

EXAMPLE 1A The grinding oil composition of Example 1 is used in anoperation of grinding aircraft engine valves composed of Inconel Xwithin the following tolerances:

Valve head radius, +0.00l" to 0.00l

Inconel X is an alloy of the following composition:

Weight 1 Element (percent) Ni 70.0 max. Cr 14.0!10 l .0. Ti. 2.25 to2.75. 0b-- 0.70 to 1.20. A1- 0.40 to 1.00. Te 9.00 max. Mn. 1.00.

The grinding operation is continued until the tolerances are exceededbecause of excessive Wheel wear. It is thereby determined that the wheellife in this particular operation is approximately 50 work pieces on therough cut and 70 pieces. on the finishing cut. The terms rough outand.finishing cut refer to the depth of cut or rate of metal removal.Thus on the rough cut all but about the last 0.005" of metal are removedquickly and in the finishing cut the last 0.005" of metal are removedslowly, the R. P. M. of the grinding wheel remaining unchanged.

The following examples are given to demonstrate the eflect of omittingeither the sulfur or the pyrophosphatidic acid from the formulation ofExample 1.

EXAMPLE 2 A composition is prepared according to Example 1 except thatthe sulfur is omitted from the formulation. The resultant composition isused as a grinding oil in the procedure of Examples 1A. The wheel lifethereby obtained is only 8 to 12 pieces as compared with the 50 to 70pieces obtained by the use of the grinding oil of this invention.

EXAMPLE 3 A composition is prepared in accordance with the procedure ofExample 1 except that the pyrophosphatidic acid is omitted from theformulation. The composition is subjected to a grinding test inaccordance with the procedure of Example 1A. The wheel life obtained is26 pieces on a rough grain cut and 30 pieces on a H finished grain cut.

The following table is a compilation of Examples 1 through 3 and ispresented for ease of comparison.

The type of oil base described in the examples is preferably comprisedof two mineral oils of widely divergent viscosities. One of the oilsshould have a relatively low viscosity of not over 100 SUS at 100 F. andmay be, for example, a shale oil or conventionally refined neutral oil.The one restriction is that it should not be so light as to flash undergrinding conditions. The other oil should have a relatively highviscosity in the range of 2000 to 6000 SUS at 100 F. (Generally theviscosity is measured at 210 F. and that at 100 F. calculated in amanner well-known in the art.) This heavier oil may be, for example, aso-called bright stock and the following are given as examples with theviscosities at 100 F. and 210 F.:

SUS at 210 F... SUS at 100 F."

These heavy viscosity oils are also characterized by their high boilingpoint.

This oil base should preferably comprise from about 53 to 95 weight percent of the low viscosity oil and from about 47 to weight per cent ofthe high viscosity oil. These proportions are subject to the furtherqualification that they be selected within the above ranges so that themixture of oil should have a viscosity in the range of 150 to 300 SUS at100 F., in order that the oil may flow properly as it is fed to thewheel during grinding. The above oil mixture should comprise at least90% of the base oil, since the presence of about of other oils oroil-like components does not interfere with the beneficial results froma composition, the major portion of which is made in accordance withthis invention. A very similar type of oil base is further described inU. S. Patents Nos. 2,453,708 and 2,453,709.

Although the oil base described above, when used as an ingredient of thecompositions of this invention, is productive of especially goodresults, it is also possible to employ other grinding oil bases. Suchbases in general are hydrocarbon oils of lubricating viscosity andproduced by any of the known methods of refining. Thus there may beemployed either singly or in admixture, solvent-extracted oils,conventionally refined oils or any other oil that has been found usefulfor grinding operations. The addition of both pyrophosphatidic acid andsulfur to any of such oils results in the improvement of the propertiesof the oil when used in grinding operations.

Several of the grinding oils of this invention were tested in practicalgrinding tests by industrial companies using commercial grinding oilsand it was found that those of this invention showed marked superiorityin practical grinding operations.

The superiority of the grinding oil compositions of this invention isobscure in theory. It is explainable in the light of present knowledgeonly by the premise that there occurs a synergistic effect between thecombined activities of the two additives, sulfur and pyrophosphatidicacid. As far as is known, there occurs no chemical reaction between thetwo additives or between the additives and the oil. It is believed thatthe improved results obtained herein may be attributed to a physicalphenomenon traceable to the combination of additives.

It is intended to cover all changes and modifications in the examples ofthis invention, herein chosen for purposes of illustration, which do notconstitute departure from the spirit and scope of the appended claims.

I claim:

l. A composition comprising at least 88% by weight of a mineral oil basehaving a viscosity in the range of 150 to 300 SUS at 100 F., from about0.5 to about 10% by weight of pyrophosphatidic acid and from about 0.25to about 3.0% by weight of dissolved sulfur.

2. A mineral grinding oil composition comprising at least 88 weight percent of a base oil which is composed of at least 90 weight per cent of amixture of an amount of a mineral oil of not over 100 SUS at 100 F.within the range of 53 to weight per cent and an amount of a mineral oilof 2000 to 6000 SUS at F. within the range of 47 to 5 weight per cent toprovide a viscosity in the range of to 300 SUS at 100 F. and from about0.5 to about 10% by weight of pyrophosphatidic acid and from about 0.25to about 3.0% by weight of dissolved sulfur.

3. A method of grinding which comprises grinding metal with an abrasivein the presence of a grinding oil comprising at least 88% by weight of amineral oil base having a viscosity in the range of 150 to 300 SUS at100 F., from about 0.5 to about 10% by weight of pyrophosphatidic acid,and from about 0.25 to about 3.0% by weight of dissolved sulfur.

4. A method of grinding which comprises grinding metal with an abrasivein the presence of a grinding oil comprising at least 88 weight per centof a base oil which is composed of at least 90 weight per cent of amixture of'an amount of a mineral oil of not over 1.00 SUS at 100 F.within the range of 53 to 95 weight per cent and an amount of a mineraloil of 2000 to 6000 SUS at 100 F. within the range of 47 to 5 weight percent to provide a viscosity in the range of 150 to 300 SUS at 100 F. andfrom about 0.5 to about 10% by weight of pyrophosphatidic acid and fromabout 0.25 to about 3.0% by weight of dissolved sulfur.

References Cited in the file of this patent UNITED STATES PATENTS2,138,546 High Nov. 29, 1938 2,339,371 Becker Jan. 18, 1944 2,396,345Rogers Mar. 12, 1946 2,431,652 Trueger Nov. 25, 1947 2.670.330 ClarkFeb. 23, 1954

1. A COMPOSITION COMPRISING AT LEAST 88% BY WEIGHT OF A MINERAL OIL BASEHAVING A VISCOSITY IN THE RANGE OF 150 TO 300 SUS AT 100*F., FROM ABOUT0.5 TO ABOUT 10% BY WEIGHT OF PYROPHOSPHATIDIC ACID AND FROM ABOUT 0.25TO ABOUT 3.0% BY WEIGHT OF DISSOLVED SULFUR.